In Mahan v. United States, the Supreme Court considered whether a federal court had jurisdiction to hear an appeal from a decision of the Commissioner of Patents in denying a patent application. The petitioner argued that the Patent Act gave him exclusive right to bring his case before any other tribunal than that provided by Congress for such cases and therefore he should be allowed to appeal directly to the Supreme Court without going through lower courts first. The Court held that it did not have original jurisdiction over appeals from decisions of administrative agencies like the Commissioner of Patents and thus could not entertain this particular petition. Furthermore, it found no evidence in either statute or common law which would give petitioner's argument merit; instead, they concluded that Congress intended all appeals involving patents go through circuit courts as prescribed by law. Thus, Mahan was denied his request for direct review by the Supreme Court on this matter

In the case of Mahan v. United States, the Supreme Court was asked to decide whether a federal statute that allowed for military personnel to be tried by court-martial instead of civilian courts violated Article III and the Fifth Amendment of the Constitution. The majority opinion held that Congress had authority under its war powers to pass such legislation, but Justice Field dissented from this decision. He argued that allowing military personnel to be tried in non-civilian courts undermined fundamental principles of due process and equal protection under law as guaranteed by both Article III and the Fifth Amendment. Furthermore, he noted that there were no safeguards in place to ensure fairness or impartiality when trying members of the armed forces before a court martial panel composed entirely of their peers. In conclusion, Justice Field believed it was unconstitutional for Congress to allow military personnel accused of crimes committed while on duty or off duty away from their post locations could not receive fair trials if they were subject only to court martial proceedings without any other form civil judicial review available as an alternative option.